This invention relates generally to material handling systems, including sortation systems, monorail systems and the like and more particularly to navigation and/or communication systems for material handling systems.
Automatic guided vehicles, or AGVs for short, are used extensively today in a wide variety of material handling applications. AGVs come in a wide variety of types, from those that carry cargo on their back, to those that tow trains of cargo behind them on carts, to still other types. In order for each AGV to be able to automatically guide itself throughout a factory or plant, it must be able to determine its position within the factory. In the past, the determination of the vehicle""s position has been carried out in several different ways. Some AGVs use laser targets positioned at known locations throughout the factory to reflect a laser beam emitted from the AGV. The reflection of the laser beams are detected by the AGV and used to determine the position of the AGV relative to the targets. Using three or more targets, the vehicle can then calculate its position. An example of such a prior art AGV system is disclosed in U.S. Pat. No. 4,790,402 issued to Field et al., the disclosure of which is hereby incorporated herein by reference.
In another type of AGV, the vehicle uses a combination of incremental sensors and one or more beacon sensors to determine its position. The incremental sensors detect changes in the vehicle""s position or bearing, while the beacon sensors make absolute measurements of the vehicle""s position or heading with respect to one or more fixed beacons positioned throughout the factory. By combining the use of both incremental and beacon sensors, the vehicle is able to determine its position and/or heading sufficiently often and with sufficient accuracy to guide itself to its intended destination. Examples of incremental sensors used on AGVs include wheel encoders that measure the rotations of one or more wheels on the AGV, and gyroscopes that measure changes in the vehicle""s orientation. Examples of beacons include magnets buried in the floor, transponders positioned at known locations, laser targets such as those described above, and various other detectable marks or objects. One prior art AGV system that uses wheel encoders, a gyro, and magnets positioned in the floor for navigation is disclosed in U.S. Pat. No. 5,281,901 issued to Yardley et al., the disclosure of which is hereby incorporated herein by reference.
In the past, the various types of AGV systems have each suffered from certain disadvantages. In virtually all of the prior AGV systems, the measurement of the position of the beacons during their installationxe2x80x94whether they are magnets, transponders, reflectors, or other typesxe2x80x94has often been a labor-intensive and expensive task. In addition, with respect to the laser-reflector AGVs, these systems require a visual line-of-sight between the vehicle and the target which can often be difficult to obtain in a crowded factory or plant environment. The use of magnets or transponders buried in the floor requires drilling or other operations that can be disruptive to the operation of the factory, and which can have significant costs. Further, the magnets or transponders must be placed on or adjacent to the vehicle pathways in order for the vehicle to be able to detect them. Changes in the pathway therefore often require the installation of additional magnets.
In addition to the foregoing disadvantages of the various navigation systems, prior art AGV systems have also had certain disadvantages in their communications systems. For example, some prior art AGV systems rely on a central controller or repeater that issues or repeats communications received from vehicles. In such systems, the vehicles do not directly contact each other, but instead channel their messages to the central controller or repeater. If a communications failure occurs with the central controller or repeater, then the whole communications system fails. Such single point of failure communication systems are desirably avoided, if possible. Additionally, prior art AGV systems have often used RF communications which are susceptible to interference, especially in plants that have extensive metal structures and electrical/electronic equipment that may emit its own radiation. These problems are also desirably avoided. The need can therefore be seen for an AGV system which overcomes the aforementioned disadvantages.
Prior AGVs have also typically included one or more bumpers on their front and/or back ends that allow the vehicle to safely stop or slow down when objects in its path are detected. Such bumpers may consist of a physical structure that produces an electric signal when impacted, optical sensors that optically detect obstacles in the vehicle""s path, laser sensors that detect laser signals emitted from the vehicle and reflected off of obstacles, or combinations of these various types of sensors. One such system is described in more detail in U.S. Pat. No. 5,048,637 issued to Lomasney. While such systems have proven to be adequate, they are often expensive to implement. Furthermore, their detection range for detecting obstacles is often limited such that it is possible for small objects to escape detection by the sensor and possibly cause damage to the vehicle, the undetected object, or both. More inexpensive sensors with a broader field of vision are therefore desirable.
In addition to the use of AGVs to move material between different locations within a warehouse, conveyors and other types of material handling equipment are often used. In order to ensure that the materials are properly moved to their intended destination, they often include a bar code on one of their sides. These bar codes are read by a scanner which is in communication with the appropriate control circuitry to ensure that, after reading the bar code, the material handling system will deliver the article to its intended destination. In order for the bar code scanner to work properly, it is often necessary to make sure that all of the articles are properly oriented so that their bar codes can be read by the scanner. Further, it is often necessary to re-scan articles whose bar codes have become covered in dirt, wrinkled, or otherwise unreadable. A method of tagging articles such that these and other difficulties could be overcome is also desirable.
Sortation systems, such as of the type described in commonly assigned patent application Ser. No. 10/163,788 filed Jun. 6, 2002 by Zeitler et al., use a distributed control having modules that are distributed along a conveying surface. The relative position of the modules is often desirably known so that a higher level controller can properly control the various components of the conveyor system. In the past, the relative position of such components was often determined by normal surveying or measuring technologies. Those techniques are labor-intensive and expensive. A method of reducing those costs is therefore desirable.
Material handling systems that employ overhead electrified monorails to transport material typically use hard-wired communications to communicate with a master controller. These hard wire connections decrease the ease at which the system is installed and/or modified. These systems also typically employ relatively expensive sensors for allowing the monorail vehicle to determine when it has arrived at a particular workstation. The desirability of overcoming these and other disadvantages can be seen.
Accordingly, the present invention provides improved material handling methods that overcome the aforementioned disadvantages, as well as others. The present invention includes a material handling system that utilizes high frequency radio location transmitters and receivers, also known as transceivers or beacons, for use in navigation, communication, and/or guidance. The use of these types of transmitters and receivers eases the installation of the material handling systems, enhances the ability of the particular types of material handling systems to determine position, and allows for improved guidance of the material handling vehicles. The present invention also includes high-frequency radio tags that can be attached to articles, pallets, or other containers for tracking, routing, and monitoring of material movement in a material handling system.
According to one aspect of the present invention, a navigation system for determining the location of an automatic guided vehicle is provided. The navigation system includes a plurality of electromagnetic energy emitting beacons which are positioned at known locations in a factory or plant. At least one electromagnetic energy sensor is provided on-board the vehicle and is capable of detecting signals from the plurality of beacons, or emitting signals to the beacons. A processor in communication with either said sensor, said beacons, or both determines location of the sensor with respect to the beacons based upon the electromagnetic signals passed between the sensor and the beacons.
According to another aspect of the present invention, a kit may be provided for modifying the navigation system of an automatic guided vehicle that uses one or more incremental navigation sensors in combination with at least one beacon sensor to estimate the vehicle""s position. The beacon sensor is adapted to detect beacons positioned at known locations. The kit includes a plurality of electromagnetic energy emitting beacons for positioning at known locations throughout an environment. At least one electromagnetic energy sensor is also included in the kit. The sensor is to be placed on a vehicle and it adapted to detect the signals emitted from the plurality of electromagnetic energy emitting beacons. The kit further includes a controller adapted to use the one or more incremental navigation sensors in combination with the detected beacon signals to generate an estimate of the vehicle""s position.
According to another aspect of the present invention, a method is provided for installing an AGV system within an environment. The method includes providing a plurality of electromagnetic energy emitting beacons and at least one automatic guided vehicle that includes at least one sensor for detecting transmissions from the plurality of beacons. At least three of the beacons are placed within the environment in a roughly triangular geometry and the location of the beacons are measured. Thereafter, additional beacons are placed in the environment and the measured beacons are used to determine the location of the additional beacons within the environment. The position of the additional beacons is communicated to the automatic guided vehicle.
According to yet another aspect of the present invention, an automatic guided vehicle is provided that includes a body, at least one navigation sensor, a motor, an ultra-wideband radar, and a controller. The ultra-wideband radar is capable of detecting objects located off of the vehicle, and the controller is adapted to control the movement of the vehicle based, at least partially, on any objects detected by the ultra-wideband radar.
According to still another aspect of the present invention, a communications system is provided for an automatic guided vehicle. The communications system includes an ultra-wideband transmitter positioned on the vehicle that transmits information from the vehicle via ultra-wideband signals, and an ultra-wideband receiver positioned on the vehicle that receives information transmitted via ultra-wideband signals from other sources.
According to still another aspect of the present invention, a material handling system is provided that includes a plurality of automatic guided vehicles with ultra-wideband communication systems. At least one ultra-wideband transmitter is positioned on or adjacent to a load of material to be moved by one of the plurality of vehicles. The transmitter is adapted to transmit a message to the plurality of vehicles indicating that the load of material is to be moved to a destination. A controller is also provided and adapted to determine which of the plurality of automatic guided vehicles is to retrieve the load in response to the message.
According to yet another aspect of the present invention, a plurality of high-frequency electromagnetic energy tags are positioned on articles within a facility. As these articles are moved, a sensor reads the information contained in the tags and uses the information to determine where the articles are to be moved within the facility. The sensor reads the information contained in the tags by a unique pattern of reflection of the electromagnetic energy emitted by the sensor toward the tags.
The AGVs, communications systems, navigation systems, and other aspects of the present invention provide various improved features for material handling systems. Among these improved features are reduced costs, better control of material movement, easier installation of material handling systems, such as AGV systems, improved communications ability, more flexible usage of material handling equipment, and increased safety. These and other benefits of the present invention will become apparent to one skilled in the art in view of the following description when read in conjunction with the accompanying drawings.